Method of destroying undesirable vegetation



United States Patent 3,012,871 METHOD OF DESTRUYING ESRABLE VEGETATIGNSidney B. Richter, Qhicago, 112., assignor to Velsicol ChemicalCorporation, Chicago, EL, a corporation of Illinois No Drawing. FiledSept. 15, 1958, Ser. No. 750,877 Claims. (ill. ll-2.6)

This invention relates to new herbicidal compositions of matter. Morespecifically, this invention relates to the control of undesirable plantlife with 2-methoxy-3,5- dibromobenzoic acid, its anhydride, its amides,its esters, its alkali metal salts, or its amine salts. 2-meth0xy-3,5-dibromobenzoic acid, which has the structure COOH Br Br will hereinafterbe referred to as compound I. This chemical compound and its derivativesas cited above have marked activity as herbicides useful for the controlof undesirable plant life.

Compound I is prepared readily and in good yield by treatment of analkali metal salt of 3,5-di-bromosalicylic acid with dimethyl sulfate.The reaction is carried out in aqueous solution, which is prepared bytreating each mole of 3,5-dibromosalicylic acid with at least two molesof an alkali metal hydroxide dissolved in water. Alkali metal hydroxidessuch as sodium or potassium hydroxide are suitable. The solution of thealkali metal salt of 3,5-dibromosalicylic acid is treated with a minimumof one mole of dimethyl sulfate for each mole of the starting compound.In practice, the use of an excess of dimethyl sulfate is preferred.During the addition, it is desirable to maintain the reactiontemperature at from about 10 to about 100 C., with external cooling ifnecessary. After addition of all the dimethyl sulfate, the reactionmixture isheated at reflux temperature to complete the reaction. Thereaction is ordinarily complete in a few hours. The reaction mixture isthen treated with a fresh aqueous solution of alkali metal hydroxide andagain refluxed for several hours to hydrolyze any carboxylic acid esterwhich may have formed as a cornpeting reaction during the formation ofthe methyl ether. The cooled reaction mixture is then acidified to Congored indicator, and the precipitated acid is filtered oif. Although thecrude acid so obtained is suitable for many herbicidal uses as such, itcan be purified if desired.

The anhydride of compound I is prepared by the removal of one moleculeof water from two molecules of compound I as the free acid. In practice,it is convenient to prepare the anhydride by the acylation of the freecarboxylic acid by its acid halide in the presence of a strong acylatingagent such as pyridine. Thus a mixture of dry pyridine and dry benzeneis treated with 1 mole of the acid chloride of compound I. The slightlyexothermic reaction proceeds with the formation of an intermediatepyridinium salt. One mole of compound I as the free acid is then added,the precipitate of pyridine hydrochloride is removed, and the anhydrideof compound I is isolated by removal of the benzene.

The acid halide of compound I required in the above and other synthesesis prepared by the reaction of the free acid with a phosporus .trihalidein the conventional manner. Thus the treatment of compound I withphosphorus trichloride until the reaction ceases produces the acidchloride of compound 1.

Compounds which are salts, esters, or amides of compoundl can beprepared readily from the free acid. Thus,

3,12,871 Patented Dec. 12, 1961 treatment of the free acid with ammoniumhydroxide gives a product which is the salt ammonium 2-methoxy-3,5-dibromobenzoate. Similarly, an alkali metal salt of compound I canbe made by the treatment of the free acid with bases, such as thehydroxides, of alkali metals. Treatment of the acid with sodiumhydroxide thus gives the salt sodium 2-methoxy-3,S-dibromobenzoate asthe product, while the use of potassium hydroxide gives the saltpotassium 2-methoxy-3,S-dibromobenzoate.

Amine salts of compound I are prepared by the addition of the free acidto various amines. Typical amines which can be used to prepare suchamine salts are dirnethylamine, trimethylamine, triethylamine,diethanolamine, triethanolamine, isopropylamine, morpholine, and thelike. The resulting products are, respectively, the dimethylamine,trimethylamine, tn'ethylamine, diethanolamine, triethanolarnine,isopropylamine, and morpholine salts of 2-methoxy-3,S-dibromobenzoicacid.

Esters of compound i are prepared by the condensation of the acid withvarious alcohols. Thus the condensation of methyl alcohol with compoundI gives the desired ester, methyl 2-methoxy-3,S-dibromobenzoate. Othertypical alcohols which can be used are propyl, isopropyl, n-butyl,sec-butyl, isobutyl, tert-butyl, amyl, hexyl, heptyl, octyl, nonyl,decyl, and the like. The products are the corresponding alkyl esters ofZ-methoxy- 3,5-dibromobenzoic acid. Although such complex esters asthose prepared by the esterification of compound I with butoxyethanol,propylene glycol butyl ether, and the like are useful products inaccordance with this invention, preferred esters are those in which theesterifying group is an unsubstituted alkyl group which contains from 1to 10 carbon atoms. The condensation of the acid with the alcohol iscarried out suitably in an inert solvent such as an aromatic hydrocarbonand in the presence of a few percent by weight of an acid catalyst suchas p-toluene-sulfonic acid. The water which forms during theesterification reaction can be removed continuously in many cases fromthe reaction mixture by distillation as it forms, and its volume can bemeasured to determine when the esterification is complete. The ester isthen isolated by distillation of the inert solvent.

Amides of compound I can be prepared conveniently by the reaction of theacid halide of compound I with ammonia or various amines. The reactioncan be carried out in an inert solvent such as ether or benzene.Preferably two moles of the amine are used for each mole of the acidhalide employed, since the hydrogen halide released during the reactionis taken up by some of the free amine which remains. The simplest amide,2-methoxy-3,5-dibrornobenzamide, can be prepared by the reaction of theacid chloride of compound I with ammonia, either as the free gas or asan aqueous solution. This amide can also be prepared by hydrolysis ofthe corresponding nitrile. Substituted amides are prepared by thereaction of the acid halide of compound I with amines such as any of theprimary or'secondary amines suggested above for the preparation of theamine salts of compound I. Thus, for example, the reaction of the acidchloride of compound I with methylamine, butylamine, decylamine, ordiethylamine gives the N-methyl-, N-butyl-, N-decyl-, orN,N-diethyl-2-methoxy-3,S-dibromobenzamides, respectively. While morecomplex amines such as the aromatic amines can be used as the aminereactant to give desirable products, which are specifically named asanilides, preferred amine reactants are alkylamines containing up to 10carbon atoms.

For practical use as herbicides, the compounds of this invention areformulated with inert carriers to obtain proper concentrations and tofacilitate handling. For example, these compounds can be formulated intodusts by combining them with such inert substances as talc or clays. Thealkalimetal salts of compound I are particularly suited to such dustformulations, and dusts containing from 5 to percent by weight of activecompound are convenient for use in the field. The compounds of thisinvention, however, are preferably applied as sprays. These can be madeas simple solutions by dissolving the compounds in organic solvents suchas xylene, kerosene, or the methylated naphthalenes. The esters ofcompound I, which ordinarily are liquids at room temperature, areparticularly suited to formulation by this method. The amine salts ofcompound I often show good solubility in water and can be used directlyas aqueous solutions.

The compounds of this invention can also be emulsified or suspended inwater by the addition of emulsifiers and wetting agents. Theformulations of these active herbicidal compounds are either applieddirectly to the plants to be controlled, or the soil in which the plantsare growing can be treated. Substances such as other pesticides,stabilizers, activators, synergists, Spreaders and adhesives can beadded to the formulations if desired. There is no significant differencein effect from the amount of water or organic solvent for diluting theseherbicides,

providing the same amount of chemical is distributed evenly over a givenarea. Such distribution can be obtained, for example, with low-pressure,low-volume sprays at the rate of about 10 gallons of spray per acre.

In applying the herbicidal compounds, consideration must be given to thenature and stage of growth of the crop, the species of weeds present,the stage of growth of the weeds, environmental factors influencing therate and vigor of the weed growth, weather conditions at the time ofapplication and immediately following, and the dosage to be applied to agiven area. Weeds are most susceptible when they are small and growingrapidly. Early application, therefore, results in better control withless chemical and increased yields because of the early destruction ofthe competing weeds. The larger and older the weeds the higher theconcentration needed to kill them. Summer annuals such aslambs-quarters, pigweeds, cocklebur, and sunflower should be sprayedwhen they are less than 4 inches high. Winter annuals such as variousmustards, fan-weed, yellow star-thistle, and wild radish are most easilykilled while they are still in the rosette stage. Usually weeds growingrapidly under optimum conditions are relatively susceptible, whereasthose growing under adverse conditions tend to be resistant to theherbicidal sprays.

The effectiveness of the compounds of this invention in small quantitiesmakes them economically sound for Weed control on large areas, with agreat saving in labor and cost, in addition to corresponding cropincreases. These compounds are particularly valuable in weed controlbecause they are harmful to many weeds but harmless or relativelyharmless to some cultivated crops. Minute quantities in contact withplant tissues may be absorbed and translocated to all parts of theplant, causing striking changes in the form and functions and oftenresulting in their death. The actual amount of compound to be useddepends on a variety of factors but is influenced primarily by thespecies of undesirable plant to be controlled. Thus While fractions of apound of actual compound I or its equivalent of an ester, salt, amide,or

the anhydride of compound I are often sufficient for postemergence weedcontrol on an acre of corn, seed flax, perennial grass seed crops,pastures or grazing areas (without legumes), wheat, and the like, theparticular species of weeds encountered in evergreen and deciduousdormant nursery stock, nursery conifers, waste areas, woody brush, andthe like may require the use of one or more pounds of compound I or itsderivatives per acre for good control. Dosage adjustments with thelow-volume, lowpressure applications suggested can be made by changingthe nozzle size, nozzle spacing, pressure, or traveling rate of thespray equipment.

The manner in which the herbicidal compounds of this invention can beprepared and utilized is illustrated in the following examples:

EXAMPLE 1 Preparation of 3,5-dibrom0salicylic acid 3,5-dibromosalicylicacid, melting point 228 C., can be prepared by the treatment ofsalicylic acid with hydrogen bromide as described by A. Leulier and L.Piuet in the Bull. soc. chim., vol. 41, pp. l362-70 (1927).

EXAMPLE 2 Preparation of 2-methoxy-3,5-dibrom0benzoic acid (compound I)3,5-dibromosalicyclic acid (50 g.; 0.17 mole) was dissolved in asolution of sodium hydroxide (27.2 g.; 0.68 mole) in 160 ml. water in a500 ml., 3-necked flask fitted with a reflux condenser, mechanicalstirrer, and internal thermometer. The solution was cooled to 20 C., anddimethyl sulfate. (43 g.; 32 cc.; 0.34 mole) was added. The mixture wasstirred for 20 minutes below 35 C., with external cooling. A secondportion of dimethyl sulfate was added, and the mixture was stirred for10 minutes below 45 C. The mixture was then refluxed for 2 hours, and asolution of sodium hydroxide (14 g.) in 40 ml. water was added. Themixture was refluxed for 2 hours, cooled, and acidfied to Congo redindicator with hydrochloric acid. The white precipitate was extractedwith two 500 ml. portions of ether. The ether extracts were dried overanhydrous magnesium sulfate and filtered.

The white solid which remained after distillation of the Preparation ofthe sodium salt of compound I Compound I (0.5 mole) is dissolved in 500cc. of methanol and treated with a solution of sodium hydroxide (20 g.;0.5 mole) in cc. of methanol. The methanol is removed by distillation invacuo on the Steam bath, and the solid residue is slurried with 100 cc.of cold, dry ether, filtered, pressed dry, and dried completely in avacuum oven to give the desired sodium salt of compound 1.

EXAMPLE 4 Preparation of the ammonium salt of compound I Treatment ofcompound I (0.5 mole) in 500 cc. of methanol with 34 cc. of commercialconcentrated ammonium hydroxide according to the method given in theprevious example gives the desired ammonium salt of compound I.

EXAMPLE 5 Preparation of the dimethylamine salt of compound 1 EXAMPLE 6Preparation of the diethanolamine salt of compound I In the mannerdescribed in the previous example, compound i (0.5 mole) is treated withdiethanolamine (52.5 g.; 0.5 mole) in 500 cc. of dry ether. The productwhich is isolated is the diethanolamine salt of compound I.

EXAMPLE 7 Preparation of the morpholine salt of compound I Preparationof the ethyl ester of compound 1 Compound I (0.5 mole), ethyl alcohol(23 g.; 0.5 mole), and 3.0 g. of p-toluenesulfonic acid are dissolved in500 ml. of benzene, and the solution is placed in a 1-liter,round-bottomed flask fitted with a reflux condenser and a calibratedDean-Stark tube. The solution is heated at reflux temperature until 9cc. of water have been collected in the Dean-Stark tube. The cooledreaction mixture is then extracted twice with 50-cc. portions of 10%sodium carbonate solution, and filtered. The benzene is distilled off invacuo on the steam bath, and the residue is then distilled in vacuo togive the desired ethyl ester of compound I.

EXAMPLE 9 Preparation of the decyl ester of compound I compound I.

EXAMPLE 10 Preparation of the n-butyl ester of compound I The reactionof compound I (0.5 mole) and n-butyl alcohol (37 g.; 0.5 mole) by themethod described above for the preparation of the methyl ester is usedto prepare the n-butyl ester of compound I.

EXAMPLE 11 Preparation of the acid chloride of compound I Compound I (1mole) is placed with 500 cc. of dry benzene in a 2-liter, 3-necked,round-bottomed flask fitted with a mechanical stirrer, reflux condenser(calcium chloride tube), and dropping funnel. Phosphorus trichloridc(123 g.; 0.9 mole) is added slowly dropwise with vigorous stirring whilethe reaction flask is cooled with cold water if necessary to control thereaction. When all the PCl has been added and the evolution of hydrogenchloride has ceased, the reaction mixture is then transferred todistillation apparatus, and the solvent is distilled off. The residue isthen distilled in vacuo to give the desired acid chloride of compound I.

EXAMPLE 12 Preparation of the amide of compound I One mole of the acidchloride of compound I is placed with 500 cc. of dry benzene in al-liter, 3-necked flask fitted with a reflux condenser, mechanicalstirrer, and a gas inlet tube having a sparger tip. The mixture isstirred while dry ammonia gas is passed into the mixture for severalhours. When the ammonia gas is no longer taken up, the precipitated saltis filtered off and extracted twice with 100 ml. portions of ether. Theether extracts and benzene filtrate are dried over magnesium sulfate andfiltered, and the solvents are distilled oif to give the desired amideof compound 1.

EXAMPLE 13 Preparation of the N-n-decylamide of compound I One mole ofthe acid chloride of compound I and 500 ml. of dry benzene are placed ina 2-liter, S-necked,

round-bottomed flask fitted with a mechanical stirrer, reflux condenser,internal thermometer, and dropping funnel. n-Decylamine (314 g.; 2.0moles) in 250 ml. benzene is added dropwise with vigorous stirring. Whenall the amine has been added, the reaction mixture is refluxed for 2hours, and cooled, after which the precipitated salt is filtered oh" andextracted with two ml. portions of ether. The ether extracts and benzenefiltrate are dried over magnesium sulfate and filtered. Distillation ofthe solvents gives the desired Nn-decylamide of compound 1.

EXAMPLE 14 Preparation of the N,N-diethylamide of compound 1 One mole ofthe acid chloride of compound I is treated with diethylamine (146 g.;2.0 moles) in the manner and apparatus described in the previous exampleto give the N,N-diethylamide of compound I.

EXAMPLE 15 Preparation of the anhydride of compound 1 Dry pyridine (158g.; 2.0 moles) and one liter of dry benzene are placed in a 2-liter,3-necked, round-bottomed flask fitted with a dropping funnel, mechanicalstirrer, reflux condenser, and internal thermometer. One mole of theacid chloride of compound I, which is prepared as described in aprevious example, is added rapidly with stirring to the reactionmixture. Compound I (1 mole) is then added in portions over a period ofabout 10 minutes with rapid stirring. The pyridine hydrochloride whichprecipitates is filtered off, and the benzene is distilled from thefiltrate in vacuo. The residue contains the desired anhydride ofcompound I, which can be purified by crystallization from a suitablesolvent.

EXAMPLE 16 Preparation of an emulsifiable concentrate of compound I Thefollowing concentrate is prepared by mixing the ingredients intimatelyin the given percentage proportions by weight:

1 Percent Compound I 25 Antarox A-400 40 Methanol 35 Antarox A400 is thetrade name under which a nonionic detergent of the aromatic polyethyleneglycol ether type is sold. The above concentrate is diluted with waterto the desired concentration for use.

EXAMPLE 17 Preparation of an emulsifiable concentrate of the n-butylester of compound I The following ingredients are mixed thoroughly inthe given percentage proportions by weight:

Percent n-Butyl ester of compound I 59 Xylene 10 Triton X-IOO 5 Kerosene26 Triton X100 is the trade name under which an emulsifler of the alkylaryl polyether alcohol type is sold. The above concentrate is dilutedwith water to the desired concentration for use.

EXAMPLE 18 Preparation of a dust from the sodium salt of compound I forexperimental purposesin greenhouses, andits response. to chemicals isvery similar to that observed for a wide variety of economicallyimportant species of undesirable plant life in the field.

The herbicidal activity of the compounds of this invention, for example,can be demonstrated in greenhouse experiments on young potted tomatoplants (Bonny Best variety). The compounds are formulated into 10percent wettable powders and are dispersed in water at a concentrationof 2,000 parts per million actual chemical. Ten milliliters of analiquot portion of the dispersion is added to the soil surface of thetomato plants, approximately to 7 inches tall. In order to avoid undueconcentration or accumulation of the chemical in any given area, 5 holesthe size of a pencil and about 1 inch deep are punched in the soilsurface around the shoot, and the milliliter application is dividedequally among the 5 holes. Three plants are used for each application.The treated plants are held under greenhouse conditions for 7 days,provided with subterranean watering, and observed for response totreatment. The results indicate a high order of herbicidal toxicity ofthe compounds of this invention.

I claim:

1. A method of destroying undesirable plants which comprises contactingsaid plants with a herbicidal composition comprising an inert carrierand as the essential active ingredient, in a quantity which is injuriousto said plants,,a compound selected from the group consisting of2-rneth0Xy-3,S-dibromobenzoic acid, its esters in which the esterifyinggroup is an unsubstituted alkyl group containing from one to ten carbonatoms, its alkali metal and amine salts in which the amine componentcontains up to ten carbon atoms, its anhydride, and its amides in whichthe amine component contains up to ten carbon atoms.

2. A method as described in claim 1, wherein the compound is an alkalimetal salt of 2-methoXy-3,5-dibromobenzoic acid.

3. A method as described in claim 1, wherein the compound is an aminesalt of 2-methoXy-3,5-dibromobenzoic acid in which the amine componentcontains up to tencarbon atoms.

4. A method as described in claim 1, wherein the;

compound is an ester of 2-methoxy-3,S-dibromobenzoic acid in which theesterifying group is an unsubstituted alkyl group containing from one toten carbon atoms.

5. A method as described. in claim 1, wherein the compound is an amideof 2-methoxy-3,S-dibromobenzoic acid in which the amine componentcontains up to ten carbon atoms.

6. A method as described in claim 1, wherein the compound is2-methoXy-3,S-dibromobenzoic acid.

7. A method as described in claim 1, wherein the compound is sodium2-methoxy-3,5-dibromobenzoate.

8. A method as described in claim 1, wherein the compound is thediethanolamine salt of 2-methoxy-3,5-

dibromobenzoate.

9'. A method as described in claim 1, wherein the compound is n-butyl2-methoxy-3,S-dibromobenzoate.

10. A method as described in claim 1, wherein the compound, isbis(2-methoXy-3,S-dibrornobenzoic) anhydride.

References Cited in the file of this patent UNITED STATES PATENTS1,948,342 Dvornikofl Feb. 20, 1934 2,394,916 Jones Feb. 12, 19462,412,510 Jones Dec. 10, 1946 2,577,969 Jones Dec. 11, 1951 2,843,470Searle July 15, 1958 2,848,470 Girard et al Aug. 19, 1958 FOREIGNPATENTS 785,989 Great Britain Nov. 6, 1957 OTHER REFERENCES Nozoe et al.in Chemical Abstracts, vol. 47, 1953, cols. 6391(0) to 6392(d); vol. 49,1955, col. 3035(i).

Patel et al. in Chemical Abstracts? vol. 50, 1956, cols. 4958(0) to4959(b).

Gilman in Chemical Abstracts, vol. 34, col. 7867(5), 1940.v

Weintraub et al. in Botanical Gazette, vol. 113, March 1952, pages348-362.

Miur et al. in Chemical Abstracts," vol. 47, 1953, col. 9435( g).

Zimmerman et al. in Contributions of Boyce Thompson Institute,January-March 1952, page 423.

Zincke in Chemical Abstracts, vol. 6, 1912, col. 1753 1 Priestly et al.in Chemical Abstracts, vol. 34, 1940, col. 6248(6).

1. A METHOD OF DESTROYING UNDESIRABLE PLANTS WHICH COMPRISES CONTACTINGSAID PLANTS WITH A HERBICIDAL COMPOSITION COMPRISING AN INERT CARRIERAND AS THE ESSENTIAL ACTIVE INGREDIENT, IN A QUANTITY WHICH IS INJURIOUSTO SAID PLANTS, A COMPOUND SELECTED FROM THE GROUP CONSISTING OF2-METHOXY-3,5-DIBROMOBENZOIC ACID, ITS ESTERS IN WHICH THE ESTERIFYINGGROUP IS AN UNSUBSTITUTED ALKYL GROUP CONTAINING FROM ONE TO CARBONATOMS, ITS ALKALI METAL AND AMINE SALTS IN WHICH THE AMINE COMPONENTCONTAINS UP TO TEN CARBON ATOMS, ITS ANHYDRIDE, AND ITS AMIDES IN WHICHTHE AMINE COMPONENT CONTAINS UP TO TEN CARBON ATOMS.